Make DexFiles opened from files readonly by default, but writable during dex2oat

Bug: 9618388
Change-Id: I83f2e16ee8446a79a94a84971146d807bb0c9ee0
diff --git a/runtime/common_test.h b/runtime/common_test.h
index e2dda86..dc1f592 100644
--- a/runtime/common_test.h
+++ b/runtime/common_test.h
@@ -434,6 +434,8 @@
     filename += ".jar";
     const DexFile* dex_file = DexFile::Open(filename, filename);
     CHECK(dex_file != NULL) << "Failed to open " << filename;
+    CHECK_EQ(PROT_READ, dex_file->GetPermissions());
+    CHECK(dex_file->IsReadOnly());
     opened_dex_files_.push_back(dex_file);
     return dex_file;
   }